Showing papers on "Mott transition published in 1972"

Theory of mott transition : Applications to transition metal oxides

Abstract: We study the metal-insulator transition due to correlations between electrons using a Hubbard model. Neglecting fluctuations in charge, we only take into account fluctuations in spin density which build up magnetic moments on each site. A close analogy with binary alloys follows from this. At zero temperature, with increasing value of the ratio of the interaction between electrons U to the bandwidth W, we obtain successively a non magnetic metal, an antiferromagnetic one and an antiferromagnetic insulator. This is due, as in Slater's idea, to the exchange part of the self consistent potential which cannot have the full periodicity of the lattice. As it is possible to find a solution with lower energy and with antiferromagnetism to Hubbard hamiltonian, one can construct a self consistent solution with random but non zero moments on each site. The alloy analog of the metal insulator transition is band splitting. For large values of the ratio U/W, the material remains insulating through the Neel temperature. For intermediate values, the line boundary between a Pauli metal and a paramagnetic insulator shows that the insulating phase is favoured at high temperature because of the entropy disorder. We draw a general schematic phase diagram for the Hubbard model and we discuss the relevance of the theory to transition metal oxides. The main qualitative features are consistent with our theory.

Systematics of the breakdown of Mott insulation in binary transition metal compounds

Abstract: An attempt has been made to illuminate the intricacies of the Mott transition as applicable to binary transition metal compounds. This has been done in the light shed by recent experimental and theoretical developments taken over a wide field. The position of Mott transition has been considered with regard to the full array of binary materials offered, and the possibilities for several new systems have been indicated. The properties of materials close to either side of the transition are discussed.

Linear Symmetric H4

Abstract: Ab initio calculations have been carried out for the lowest 1Σg+ state of H4. A contracted Gaussian basis set of two s and one p functions centered on each atom was used. Self‐consistent field (SCF), SCF plus all singly and doubly excited configurations, and full configuration interaction (2172 configurations) calculations were carried out. The results may be pertinent both to the H2+D2 reaction and the problem of the linear antiferromagnetic chain. It is predicted that two H2 molecules may approach to within 1.6 bohr with an energy only 43 kcal above that of the separated molecules. A van der Waals attraction of 22°K is predicted at H2 – H2 center of mass separation 7.1 bohr. Equidistant H4 is predicted to have lowest energy at 1.67 bohr, lying 7.1 eV below the exact energy of four H atoms but 44 kcal above two H2 molecules. The electronic structure of linear equidistant H4 is discussed as a function of H – H separation and no evidence of a Mott transition is found.

Effects of Impurities on the Metal-Insulator Transition

Abstract: The effect of impurities on the critical interaction strength for the Mott transition has been investigated using an extension of the Gutzwiller approach to correlation in the metallic state. It is shown that the band narrowing due to impurities causes a reduction of the effective interaction necessary for the transition to the insulating state. The residual resistivity due to impurity scattering is considered and it is argued that the conductivity can be written as the product of the Fermi-surface area and the mean free path. Since the latter is limited by the average impurity separation the residual resistivity is bounded. This upper bound appears to be violated for Cr-doped ${\mathrm{V}}_{2}$${\mathrm{O}}_{3}$.